Telephone system.



B. M. DAVIS.

TELEPHONE SYSTEM.

APPUCAHUN FILED MAR. 5. i998. 1,146,786. Patented July 20, 1915.

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f a II B. M. DAVIS.

TELEPHONE SYSTEM.

APPLICATION FILED MARS, 1508.

1,146,786. Patented July 20, 1915.

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B M. DAVIS.

.TELEPHONE SYSTEM.

APPLECM'ION men MAR, s. was.

1, 146,786. Patented July 20, 1915.

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Affozvz wsggim 7 B. M. DAVIS.

TELEPHONE SYSTEM. APPLICATION HLED MAR. 5. 1908.

1,146,786. Patented July 20, 1915.

6 SHEETS-SHEET 5- B, M. DAVIS.

TELEPHONE SYSIEM. APPLICATION FILED MAR.5.190B.

1,146,786. Patented July 20, 1915.

6 SHEETS-SHEET E.

I I I a l l CU'Z'W Q @gf fieffiueZl'f. Dem/$51 Wee UNITED STATES PATENT OFFICE.

BETHUEL M DAVIS, 0F CHICAGO, IILLNOIS. ASSIGNOBL. BY MESNE ASSIGNMENTS, TO AUTOMATIC ELECTRIC COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

TELEPHONE SYSTEM.

Application filed March 5, 1908.

To all whom it may concern:

Be it known that I, Bnrmzm, M. DAVIS, a citizen of the United States of America, and resident of Chicago, Cook county- 111]- nois, have invented a certain new andu'seful Improvementin Telephone Systems, of which the following is a specification.

My invention relates to automatic tele' vphone exchange systems of that particular type in which the subscribers metalli-cline circuits are free from operating grounds at the substations, and inwhich the automatic switches at the exchangeare, therefore,-c0ntrolled ove-r circuits including the two sides of the subscribers lines in series, through the medium of a make-and-break device or impulse-transmitting device" included directly in the line at each substation.

My invention also relates more especially to two-wire automatic telephone exchange systems of this character in which the release or disconnection between subscribers lines is efl'ected through the medium of certain slow-acting release relays-that is to say, relays which are retained in an energized condition during conversation between the two subscribers, and which are made slow-acting to prevent a premature release during the transmission of the call, the sluggish or reluctant manner in which these relays denergize being sufiicient tooprevent them from being denergized by the brief or momentary breaking of the circuit during the transmission of the call, whereby. they only denergize to effect the release when the subscriber hangsup'his telephone and thereby opens the-line circuit as: a much longer period of time, ofcourse, than is the case duringithe'transmission of-the' call.

In systems of theforegoin general character it was found-that the ca lingsubscriber would occasionally stop or restrain the make and-break device during the transmission of the call, thus holding the line circuit open for a period of time suliicient to deenergize the said slow-acting release relays, thus bringing about a premature release of the s itch or switches. either purposely or in advertently, and necemitating a repetifion of the entire calling operation. Primarily, therefore, my invention'isaddressed to the problem of preventing a premature release of the snatches in a tW0W'll(}2lfllZ0[Ii1llflCtBl8- phone exchange svstem in which the release is effected through the medium of slow-act S ecification of Letters Patent.

Patented July 20, 1915.

Serial No. 419,302.

.rest'rained'in its-action,-but will continue in itsoperation guntil th'c"impulses haveall been properly transmitted-rarer theline, whereby the subscriber is notbnly'precluded from forcing or accelerating the transmission of said impulses-but, is also prevented or preeluded from stopping the transmission of the impulses'a'fter the make-and-break device has once started to operate under the propelling action of the spring by which it is returned to the normal position from which it was movedby the forward rotation of thecallin .dial.

In a system 0 a kind it is important that the subscriber be'precluded from forcing or accelerating the speed with which the calling impi'il'sesifla'i-e transmitted over the line, and it is equally important, where slow-acting release relays are employed in the manner explained, that the calling subscriber be precludednfrom interrupting or restraining the operation of the make-and-brea-k device at a time when the line circuit would be held open for such a period of time that the release relays would be deenergized, and a premature release thereby precipitated. With the combination of the non-forcible dial and the non-interruptible or non-restrainable lmake-a-nd-break device, as previously referred to. I am enabled to orercome both of the said dilliculties.

To the foregoing and other useful ends, therefore my invention consists in matters hereinafter set forth and claimed.

In the accompanying drawings, Figure l is a front elevation of a subscribers calling device, showing the apertured dial or rotatable portion equipped with a metal cover containing the subscribers calling figures and number-plate Fig "2 is a front elevati n of the same with the metal cover and lllOVtl ble dial removed. showing the mechanism underneath which controls and is controlled by the dial. Fig. 3 is a similar elevation but with a portion of the dial represented in position to engage the controlling lever of the impulse wheel, and showing the lever which prevents backward rotation of the dial. Fig. i shows the relative position of the mechanism represented in Fig. 3, while the dial is being rotated. 5 shows the relative positions of the parts while the mechanism as a whole returns to its original position. Fig. 6 is a rear elevation of the calling device, showing the'various features, suclr as governor, impulse wheel, a portion of the switch-hook and controlling spring, ground spring, impulse springs, etc: Fig. 7 is a side elevation of the mechanism shown in Fig. 6. Fig. 8 represents a partial crosssectiou' of Fig. 6 on line 7-7. Fig. 9 is a section showing the. device which prevents backward rotation of the dial. Fig. 10 represents'a section of the same mechanism shown Fig. 9, showing how the dial is locked after the impulse w heel has been released. Fig. 11 illus trates a subscribers station A and a portion of the exchange apparatus. Fig. 12 shows another-"subscribers station A and a still further portion of the exchange apparatus. Figs. 11 and 12 taken together illustrate an established connection between the sub scribers A and A, the subscriber A being the calling subscriber.

As thus illustrated, and referring to Fig. 6, it will be seen that the framework comprises a front plate 2and a back plate 3, the two plates being rigidly connectedtogether by the rod 4 and two screws 5. Upon this framework all of the operative parts of the calling and switch-hook mechanisms are mounted in a suitable manner. A shaft'fi (Fig. 8) extends centrally throught-he said lates 2 and 3 and is arranged-to rotate reely upon bearings. The front bearing of this shaft consists of a hub 7, grooved to difl'erent diameters, and adapted to provide bearings for the locking disk 8 (Fig.4) and the dial 9 (Fig. 1). The disk is retained in position by the metal washer 10 (Fig. 4) while the dial 9 is held in position between the said Washer 10 and the metal washer 11 supported by the screw 12, as shown in Fig. 8. Both the lockingdisk 8 and the dial 9 rotate freely upon their bearings, the disk being held normally in position by the spring 13 (Fig. 3), while the dial is symmetrical and has no normal position relative to the other mechanisms. One end of the spring 13 is fastened to the disk 8, while the other end is attached to the front plate 2. It will be understood, of course, that the said dial and disk may be secured in any other suitable and approved manner. Along the periphery of the dial 9 there is, as will be Fig.6, there is a-ciockspring 16.

observed, a series of openings, twenty-six in number, as shown in Fig. 1. Thirteen of these openings and a portion of one other are exposed through the circumferential opening on the cover-plate H, which circumferential opening determines the limit of rotation of the dial for any particular digit. The remainder of these openings or fingerholtB, with the exception of two, being represented under the coverplate, are indicated by dotted lines. On said dial plate, within the outer series of openings and on the under side of the dial, will be found a series of projections. corresponding in number to the opening-s. along the periphery, and being underthe 'cover-plateare represented by the dotted rectaiigles 15. These projections may bemaide by punchingthrough the metal dial plate 9.

Directly back of the plate 3, as shown in This spring is securedcat one end to a projection on the birek-piateiat the pointl'r', and is con fihed-within definite Limits and held. in position by the projecting arm 18 and the spring bracket 19. The inner end of the spring 16 is fastened to the shaft 6 in such a manner that. its tension, when wound, tends to rotate the shattfin a counter-clockwise direction, when viewed from the front. Mounted upon the shaft 6 there is also a gear wheel 20 arranged to rotate freely upon the shaft except when engaged by a ratchet arm, as will hereinafter appear. In addition the toothed disk or impulse .wheel 21 (Fig. 7) is fastened: to the said shaft by means of a. clamp 29.. A receiver-hook 2 3 is pivoted on the backplate 3 at the: point ZL a-ndL iIIthe front plate 2 at thepoint 25, as represented by the dotted circle inFig. 2. Said. receiver hook is arranged to have a limited. up-and-down movement when the receiver is removed'and replaced. A release cam 26 -(Eig. 6) is rigidly fastened to said hook atihe point27I At its extremity this cam 26 is providedwith. an insulating bushing 28. Then the telephone receive-r rests upon thehook, the latter being-down the arm of the cam '26- permits the spring 29 to be in contact with the spring 30; but upon removing-the receiver this cam operating upon the spring 29 by means of the bushing 28 separates it from the spring 30 and places itin contact with the spring 31. The arm 32 (Fig. 2) is pivoted to the backward extension 33 of the receiver-hook at the point 34, its extremity being engaged by the spring 35, which latter is rigidly secured to the portion or rod after passing over a projecting rod 36 of the front plate The tension of the spring tends to always keep the receiver-hook in an elevated position, which is accomplished when the receiver is removed from t e hook. Secured to the impulse wheel 21 of the calling device is a dog 37 which is held normally in contact with the teeth of the gear whee 20. As the dial is rotated in a torward direction this dog 37 passes freely over the teeth of said gear wheel. However, when the impulse wheel, relieved from the control of the d al, begins to rotate back to its normal position under tension of the spring 16, then this dog engages the gear wheel, causing it to revolve in unison with the impulse wheel, As will be observed, the said gear wheel is caused to revolve or rotate when the hook-is moved downward, or when the impulse wheel is rotated under the control of the clock-spring. The conditions thatvcause the gear wheel. to revolve when the switch; hook is moved downward will be easily understood by referring to Figs. 2, 6 and 7. The arm 52 (shown in Fig. 2 and hereinafter referred to) is rigidly connected to theshaft.

If it were not for this arm 52, which strikes the pin 53 on the rear of the switch hook, the main spring 16 shown in Fig. 6 would unwind itself, and if this spring 16 were strong enough it would prevent the switch hook from rising. The arrangement is such, however, that the switch hook spring 35, shown in dotted lines in the lower part of Fig. 2, is sutliciently strong to overcome the opposing force of the main spring 16. It is obvious, therefore, that when the switch hook has been raised the shaft is rotated to a certain extent in a clockwise direction, viewing it as shown in Fig. 2. WVhen the switch hook is depressed the shaft naturally resumes its original position," because the arm 52 follows up the stop 53. Now, since the impulse wheel :21 (Big?) is rigid with the shaft it will turn with' the shaft, and since it is provided with the dog 37 (Fig. 7) the gear wheel will be, rotated. As a matter of fact, if the switch hook is jerked down quickly the arm i 'ifif lags behind the stop 53. The teethaofmthegearwheel en gage with the teeth of apinion 38 (Fig. 7 This pinion is a part of the so-called 'governor or governing device 39 -that is, the device which controls the speed of the impulse wheel when it rotates backward after being released from the control of the dink-and, which controls the speed of the switch-hook when the latter is returned toits normal position. Upon the end of the pinion are pivoted two parts l0 and14r1 vhich, taken together, form a cylinder, the two partsbeing suitably pivoted, as part 41 at the point 42. These parts are normally held together by means of two springs (not shown), and are adapted to fit loosely upon the cupshaped ring 43 (Fig. 6), the latter being rigidly fastened to the framework of the calling device at the point 44. As the pinion 38 revolvcs rapidly when actuated by the gear wheel 20, the ends of the parts and 41 farthest away-from their respective pivotal in contact at the point 46 with a rigid arm 47. This arm is also fastened securely to theframe of the calling device, but insulated therefrom. Parallel with the spring is another spring 48 (Fig. 7) which contains a bushing .49 acting upon the spring 45 to break contact between it and the arm 47 when the impulse wheel has been operated and rotates back. On this spring 48 is a projection 50 (Fig. 6) so shaped that each impulse tooth- 51 of the impulse wheel 21 presses the spring 48 away from the spring 4:51:15 the wheel 21 is rotated forward.

Whenthe, impulse wheel returns, however, the teeth successively engage the projection 50 in a well known manner, so as to press the bushing l9 against the spring 45 and cause saidfspring to, break contact with the arm 47 once foreach impulse tooth which passes the projection 50. Fastened to the shaft directlyback of the front face plate 2 is an 52 which engages a pin 53 on the back extension 54 of the receiver-hook. This arm rotates in unison with the impulse wheel and prevents it from rotating back beyond a'certain point, owing to its bearing on said pin 53. Upon the arm 52 is a lever 55 pivoted at 56 and-having at the other end a projection 57 adapted to engage. the notched disk 8 crvlsome one of the projection 15 of the dial at the appropriate 1 time. Upon the leven55 is another cam 58pivoted at 59 and actcdupon by a spring 60. This spring normally keeps the cam 58 insucha positionlthat'its length is at right angles to the-love asshown in Fig. 3. The lock ing disk. S lras halffits circumference notched to form a regular'series of. teeth and is equippedbwith two projections 63; and 62 extending from the periphery of the other half. Between these two projections a portion .ofithe disk is bent over and downward and given an oblique edge 63 (Fig. 10), this edge acting upon the lever 61, as shown in Figs. 4 and 5. Said lever 64 is pivoted at thefpoint 65 and is guided in its movements by two pins 66 and 67 as it is depressed by the edge 63 of the disk 8, or raised bv the action of the spring 68, shown in Fig. 6. \Vhen the receiver is on the switch-hook, which is in its normal position. the projection 57 engages the projection 61 and holds the disk 8 in the position shown in Fig. 3. In this position the lever 64 is not depressed by the edge 63 of the locking disk 8. (onsequently the spring 68 acts to raise the lcver 64 sufliciently so that the portion 69 of the lever is engaged by the projections on the under side of the dial, as shown in Fig. 3, and more clearly in Fig. 10. In this manner the forward or backward rotation of the dial is prevented as long as the switch-hook is down. When the switch-hook is raised the spring 13 rotates the disk 8 until the projection 61?. comes in contact with the pin 62' and the edge 63 has again depressed the lever arm 64. he portion 69 of said arm does not have its surface parallel with the dial, but at an angle such that the portion which opposes the forward movement of the dial when the arm is raised allows the projection 15 of the dial (Fig. 10) to just pass over its edge when this arm is depressed. (See Fig. 9.) The 0 positc edge, however, which opposes the bee ward movement of the dial, is never depressed so far that it escapes the projections of the dial when an attempt is made to rotate said dial backward. When the dial is drawn down the projection 15 on the said dial nearest the projection 57 engages said projection 57, and the-portion 52 (Fig. 5) with all its parts 55 and 58 is rotated along with the impulse wheel in consequence. As soon as the-cam 58 strikes the waved edge of the front plate 2 at the point 70 it is deflected, as shown in Fig. 4, thus allowing the projection 57, as shown in Fig. 3, to still clear the teeth of the disk 8 and remain in engagement with the projection 15. The stop which limits the downward pull of the dial for any particular digit is the cover-plate 14 at the point 71. This point is so situated that the last projection on the back of the dial plate which engages the lever 64 for any particular digit is drawn a little beyond the lever 6-1. This allows sufiicient backward movementof the dial to permit the cam 58 to assume its upright position. The consequent depression of the arm 55 causes the finger 57 to engage the disk 8, at the'same time withdrawing the said finger-from enigement with the projection 15 of the dial, y means of which the rotation of the mechanism was accomplished. This, then, causes a release of the parts from the dial and allows them to return to their normal positions under the control of the clock-spring. In consequence of the projection 57 engaging said'disk 8 as the impulse wheel rotates back, said disk is carried with it. The lug 61 is raised slightly above the plane of the disk 8 in order that it may pass over the top of the pins 66 and 67. The moment this occurs the lever 64 rises and makes it impossible to rotate the dial again until the impulse wheel has returned to normal and the disk is again released. The release of said disk is effected by the cam 58 reaching the off-set in the cover-plate at the point 70, at which time the spring 60 raises the arm 55, freeing the projection 5'? from the disk, which then re turns to its original position under the in fluence of the spring 13. When the receiver is taken from the hook or replaced, the movement of the projection 57 is guided by a. projection 71 extending from the front plate. The cover-plate 14 may be fastened to the front plate 2 in any suitable manner, and may have mounted thereon in any suitable manner the series of numbers and directions, in accordance with which the subscriber may select the proper finger holes in the dial to obtain his connections. The further operation of the calling device may best be shown by the process of tracing a call from one subscriber to another through the medium of certain automatic mechanisms.

As shown, the line of substation A (Fig. 11) terminates in a line switch C. The master switch that controls the selective operations of this line switch, as well as the other line switches of the same group, is shown at D. The line switch C is a trunking switch provided with suitable bank jacks assembled to form a so-called line switch bank (not shown). Each of these bank jacks F. is the terminal of a trunk-line terminating in aselector or connector switchas here shown, in the first-selector switch F. It is to be understood, of course, that these bank jacks E are multipled with the corresponding jacks of all the other line switches of the same group. It will also be understood that when one line switch is occupying one of these jacks no other line switch can come in on the same trunk-line. The first-selector F is also a trunking switch and is provided with sets of trunk terminals each set of which may terminate in a second-selector switch, or, as in this instance, the connector switch H. As in the case of the line switch banks, corresponding terminals throughout the first-selector bank sets are multiplcd together. The line switch C allotted to sub station A is identical in construction with the line switch 0.

The substation A illustrates the calling device previously described in its capacity of calling a subscriber automatically. As shown, this substation comprises the usual receiver 72, transmitter 73, induction coil 74 with the primary winding 75 and secondary winding 76, ringer 77, switch-hook 78, and the aforesaid described impulse wheel 21. It is understood that associated with this station are all the other parts of the calling device described in the preceding. As this is a common battery system the transmitter 73 and the primary winding 75 are in series with the line conductors P21 and 192 when the subscribers are talking. The receiver T2 is in a closed local circuit in series with the scconrlarv winding 76. \Vhen the switch-hook is down the springs 29 and 30 are maintained in contact for the purpose of bridging the ringer 77 in series with the condenser 79 across the line. When the switch-hook rises on removing the receiver the springs 29 and 31 are brought into contact, thereby closing the talking circuit. The line switch 0, which is allotted exclusively to a subscriber, comprises the socalled trip ma net 80, the release magnet 81. and the bri ge-cut-ofl' relay 82 provided with the springs 83, 84, 85 and 86.

The first-selector F is a. modified form of the selector switch disclosed in United States Letters Patent No. 815,321, granted March 13, 1906, to Keith, Erickson & Erickson. It is provided with a switch shaft (not shown) carrying the line and private wipers ST. 88 and 89, a double-wound coil 90, a slow-acting private ma et relay 91, and a slow-acting releasing re ay 92. The vertical magnet 93, rotary magnet 94, release magnet 96, and the private magnet are well known. The said private magnet controls the side switch wipers 97 98, 99 and 100.

The connector switch H is a modified form of the connector switch disclosed in United States Letters Patent No. 815,176, granted March 13, 1906, to Keith, Erickson & Erickson. It is also provided with the usual switch shaft (not shown) carrying the line and private wipers 101, 102 and 103, a double-wound coil 104, and the slow-acting release and private magnet relays 105 and 106. respectively. It is further provided with an auxiliary relay 107 which operates to lock the connector side switch in second position if a busy'line is called. The vertical magnet 10S, rotary magnet 109, release magnet 110, ringer relay 111, private magnet 112, and the back-bridge relay 113 are well known. The exchange contains a ringer generator 114, an interrupter 172 for the ringer relay circuit, and an interrupter 196 for the busy transformer 195.

The line switch C, of the same construction as the line switch G, contains the release magnet 11S, trip magnet 119 and the cut-off relay 171.

Assuming this to be a one-thousand subscriber system, the substation A will be designated #220, and in order to call said substation t-he subscriber at substation A must operate his dial three times in accordance- Through the action of the trip ma net upon a plunger (not shown) the barn contact springs 125 and 126, 127 and 128, 129 and 130, and 131 and 132 are closed, as shown at E. The closing of contact between springs 1'29 and 130 completes an energizing circuit to the bridge-cut-ofi relay 82 which acts to separate the springs of said relay and thereby break the energizing circuit through the trip magnet 80 and the common relay 123. The closure of contact between the bank springs 125 and 126 and 131 and 132 extends the subscribers line conductors 121 and 122 to the trunk-line conductors 133 and 139, respectively, leading to the selector F. This results in an energizing circuit being established from ground G through the lower winding of the relay 90, side switch wiper 98, trunk conductor 133, winding 136 of the trunk relay 137, through the bank springs 131 and 132, line conductor 121, through substation A to the line conductor 122, through the bank springs 126 and 125, Winding 138 of the relay 137 to the trunk conductor 139, through the side switch wiper 97, u per winding of the relay 90 to the battery ead 124, thence through battery B to ground G. The line relay 90 is thus energized, transferring the spring 141 from contact with the spring 142 and into contact with the spring 143, and closes a. circuit energizing the slow-acting relay 92, which in turn shifts the spring 144 from contact with the spring 145 and into contact with the spring 1&6. The circuit for the slow acting relay 92 extends from ground G through the springs 141 and 1&3, relay 92 to the battery lead 124, thence through battery B to ground G. When the relay 92 energizes, as described, the line relay spring 142 is placed in connection with the slow-acting private magnet relay 91, and through said relay with the vertical magnet 93, whereby ound impulses may be sent from said spring 142 through the said magnets 91 and 93 while the relay 92 is energizcd. The trunk relay 137 being included in the same circuit as the line relay 90, energizes at the same time and separates springs 1&7 and 148. So far all this has been accomplished by the subscriber in the act of removing his receiver from the hook. He now proceeds to call by operating the dial for the first digit 2; When the dial is drawn downthe impulse wheel 21 is rotated so that two of the impulse teeth 51 are carried beyond the lug 50 on the spring 48. hen the dial is released the impulse teeth act upon the lug 50 to twice separate the spring 45 from contact with the spring 47. Each time that the said springs are separated the eneriz ing circuit for the relays 137 and 90 is interrupted, but relay 137 being slow-acting is not given time to denergize between impulses, the impulse wheel operating at a rate to produce that result. Each time that the circuit is interrupted at the springs 45 and l? the line relay 90 of the selector F falls back and permits the spring 141 to make contact with the spring 142. In this way impulses are transmitted from ground G through springs. 141 and 142 of the line relay, springs 14-1 and 146 of the relay 92, through the private magnet relay 91 and the vertical ma et 93, wlper 99 to the battery lead 124, t ence through battery B to ground G. As with relay 137, the releasing relay 92 does not have time to denergize while the line relay 90 is o crating. The first impulse transmitted by t e line relay 90 causes the private magnet relay 91 to energize, and said relay remains so during the succeeding impulses, owing to its slow-acting character. Upon being energized the said slow-acting relay 91 causes the springs 149 and 150 to make contact, which closes a circuit through the private magnet 95. The impulses produced by the line relay 90, of course, also energize the vertical magnet 93, which acts to raise the shaft one step for each impulse. Since two impulses are transmitted to the shaft, the line and private wipers S7, 88 and 89 are raised two steps and brought opposite the first contact of the second bank level of the selector F. When the impulse wheel 21 ceases to operate the spring 48,. the line relay 90, again resumes its constant energized state, so that the private magnet relay 91 denergizes, allowing the springs 149 and 150 to se arate. The private magnet 95 thus being 'energized allows the side switch to trip to second position. As soon as the side switch trips to second position the side switch wiper 99 closes an energizing circuit. through the rotary magnet 94 which, by attracting its armature, rotates the shaft one ste and places the line wipers in contact wit the first trunk-line in the second level. The rotary arm also acting upon the private magnet armature causes it to release the side switch to the third position, providing the first trunk is idle. When the side switch passes to the third position, ground is thrown upon the private wiper 89 from ground G through the springs 141 and 143 in contact, the side switch wiper 100 thus providing a guarding potential for that trunk-line. In case a trunk-line is busy, however, the shaft wipers will be carried to a trunk-line which is not occupied, in a manner well known. The shaft wipers having been rotated to a trunk-lineleading to a connector H, as here assumed, as soon as the side switch passes to the third position, the connector line relay 104 is immediately energized. This circuit extends from ground G through the winding 151 of the relay 104, over the line conductor 152 through selector F, then over a circuit previously traced through substation A over the other side of the line to selector F again, through it to the trunk conductor 153, through the upper winding of the relay 10-1 to battery lead 124, thence through battery B to ground G. The line relay acts to throw the spring 151 out of contact with spring 155 and into contact with sprin 156, closing an energizing circuit throu the release relay 105. As soon as this slow-actin relay energizes, the spring 157 is carrie out of contact with the spring 158 and into contact with the spring 159, and the spring 160 engages the spring 161. As soon as s rings 160 and 161 close in contact a guar ing potential is applied to the trunk-release conductor 162. This guarding potential maintains the slow-acting relay 92 of the selector F energized. The closure of content between the release relay springs 157 and 159 connects the line relay spring 155 with the vertical and rotary magnets 108 and 109, respectively.

lVhen the subscriber now proceeds to pull his dial for the second digit 2, the line relay 104 operates exactly as the line relay of the selector F operated, thus permitting the spring 154 to make contact with the spring 155 once for each unit of the second digit. In this manner ground impulses are imparted to the vertical magnet 108 as many times as the springs I54 and 155 are closed. In this circuit. through the vertical magnet is included the private magnet relay 106. At the first impulse the private magnet relay 106 energizes, andbei ng a slow-acting relay remains energized during the interval that the remaining are imparted to the vertical magnet. Al; the end of this operation the shaftiwipe'rs' 1'01, 102 and 103 will have been brought 0 posite the first contact of the second fleve of the connector banks. Upon energizing, the slow-acting private magnet rel'ay10l3 separates the springs 163 and 164, and 165 and 166, carrying the spring 164 into contact with the spring 165. This closes an energizing circuit through the private magnet 112. When the line relay 104 ceases to operate, the slow-acting relay 106 de'elnergizes, resulting in the denergization of the private magnet 112. U 301'] doing so the side switch (as is well lmown) passes to second position. The subscriber is then ready to operate his calling device for the last digit 0. He does so and thereby transmits ten impulses to the line relay 104, which in turn transmits an equal number of impulses to the rotary magnet through the side switch wiper 167 and contact point 168. This results in carrying the shaft wipers intoengagement with the required line in the usual manner. The private magnet relay 106 and the private magnet 11:? energize, as in the previous instance. while the impulses are being transmitted. If the called line is busy the connector side switch will be locked in second position and the calling subscriber is given a busy-signal. Vhen not busy, at the cessation of the impulses the private magnet denergizes and permits the side switch to pass to third position. When the side switch wiper 169 passes to contact 170 a guarding potential is provided at the private wiper 103 for protecting the seized line from outside interference. This potential also provides the means for energizing the cut-off relay 171 of the line switch C, thus preventing the switch 0 from operating when the subscriber at station A removes his receiver from the hook in response to a call. \Vhen the side switch 1 passes to third position the trunk-release conductor 16:2 is provided with a guarding potent al from ground G ,-a guarding potential being provided for this trunk from ground G for the first and second positions. The calling subscribers line has now been extended to the normals of the called sub scriber, and from these over the line conductors to station A. As soon as connection is thus established the ringer relay 111 is energized by a current flowing from ground G through the interrupter 172, through the back-bridge relay springs 173 and 174, ringer relay 111, conductor 175, side switch wiper 167, slow-acting relay 106 to the battery lead 124. thence through battery B to ground G. This relay 111, thus energized.

throws generator current on the called line to operate the ringer of station A. When the called subscriber answers, the backbridge relay 113 is energized by a flow of current from ground Gr through the lower winding of the relay 113 over the positive side of the line conductors, through station A back over the negative side of the line,

through the upper winding of. the relay 113,"

thence through battery B to ground G. The relay 113 energizing separates the springs 173' and 174 and breaks the circuit established from the interrupter 172 through the ringer relay 111. The subscribers are then comiected for talking over the main line conductors indicated by the heavy lines. The calling subscriber. upon removing the receiver from the hook and causing the line switch bank contacts to close by the action of the line switch plunger on the same, closes a circuit from battery B through the release magnet 81, line switch bank contacts 128 and 127 to the master switch bank contact 17S upon which. just previous to removing the receiver 72 from the book 78, rested the wiper arm 179 of the master switch D. Said wiper connects the contact 178 with the bank contact 180 which is permanently connected to ground through the winding 181 of the differential relay 182. The differential relay is constantly energizcd. but is inoperative until one of its windings is shunted. The circuit just traced shunts the winding 183 of this relay, removing the opposition of the winding to the energization of the winding 1S1, whereupon the relay operates to close the springs 18% and 185. A circuit is thereby closed through the master switch magnet which, thus energized, operates to carry the wiper 179 to the next adjacent contact of the master switch bank, and to rotate the shaft so that the plungers connected therewith stand directed to the next unoccupied trunk-line. In this way another subscriber belonging to this same group will obtain the next trunk or a trunk that is not engaged. Should the trunk in any-case be occupied, however, the wiper arm and plungers will be carried in a similar manner until a free trunk-line is obtained. After the subscribers are through talking, if the calling subscriber hangs up his receiver he opens up the line circuit at the sprin s. 29 and 31,'thereby initiating the release of all the switches. At the instant l the circuit .is broken between the said springs 29 and31 the double-wound trunk relay 137 deiinergizes, permitting the springs 117 and 148 to come into contact. This establishes an energizing circuit for the relay 187 over a path extending from ground Gr through the relay 187, springs 148 and 14:7, bank springs 127 and 128, through the release magnet 81 of the line switch C, thence through battery B to ground G. As soon as the relay 187 causes the springs 188 and 189 to' close, a release circuit is established through therelease magnet 81 from ground Gr through, the interrupter 190, said release magnet 81, through battery B and to ground G. The release, magnet energizes and attracts its armature'which, on being released; withdrawstheplunger from the line switch bank The release occurs when the release magnet" 81 is deenergized as the interrupter momentarily breaks the circuit. As soon as the plunger is withdrawn the circuit through this said magnetBl is broken at the bank springs 127 and 128. At the same time the line relay 104and'release relay 105 of the connector H de'nergize. As these deenergize an energizing circuit is closed through the release magnet 110 from ground G springs 154, 155, 157 and 158. said release magnet 110, normal springs 191 and 192, conductor 124, thence to battery B and ground G. The release magnet thus energized releases the switch shaft and side switch, thereby breaking the energizing circuit through the back-bridge relay 113. if the called subscriber has not done so first by restoring his receiver, and also the energizing circuit through the bridge-cut-ofi' re lay 171. In dropping to normal the connec- 10% and of the slow-acting relay 105 also causes the release of the preceding switches, since ground from G is interrupted by both these relays. When this occurs the releasing relay 9:2 deenergizes, and a circuit is thereby close-d through the release magnet 96. The release magnetenergizing restores the firstselector side switch and switch shaft, the latter in dropping to normal breaking the circuit through said release magnet at the normal springs. After the switches are thus restored the calling subscriber can then proceed to make another call. In case a line that is called is busy the private magnet 112 remains energized when the last rotafy=impulse connects the private wiper withia busy line, thus locking the side switch in second position. At the same timethcbacksbridge relay 113 energizes in series with the private magnet 11:2. Said relayin energizing closes a circuit through the. locking relay 107. Vhen the relay 107 energizes, thecircuit of the rotary magnet is broken. In this-mannor the subscriber is preventedirom" rotating the connector switch shaft should he attempt to operate his dial while receiving the busy-signal. It will be seen that when the I0? energizes, the circuit for maintaining the private magnet 112 energized is then shifted from the private wiper 103 to ground G. The objectof this'arrangement is to prevent the side switch from unlocking and passing to-third position, if the switch that is maintaining the called line busy should be released while the calling subscriber A is receiving the-bnsy-signal. The relay 107, upon energizing, likewise establish'esthe busy circuit asdollows: from the secondary winding of the husyucoil 195 to the positiveside of the line, through substation A to the negative si'dcof the line, through the interrupter 196,.winding of the busy coil 195, back to the'se'condary winding. lVhen the calling subscriber receives the busy-signal he understands'thatthe line is busy and hangs up hisreceiver.v :The line circuit is open, as already explained, with the result that the line and slow-actin relays 104 and 105 ofthe' connector If deenergize, causing the release of the connector and all other switches, as heretofore ex plained.

From the foregoing it will be seen that I proyide a two-wire automatic telephone ex change system in which the release is eflected through the medium of slow-acting release relays. and in which the calling subscriber is precluded from stopping or interrupting the calling operation in a manner which would hold the line circuit open for an unduly long period 0f time-that is to say, for such a period of time as would result in a premature deenergizing of said relays and consequent release of the connection. The dial, owing to the provision of the dial-locking device, is of a non-forcible character that is to say, it cannot be moved in such manner as to force or accelerate the transmission of the impulses, as it is locked against backward rotation, at least at any time that the calling subscriber should attempt to force it in a backward direction. A very slight backward motion of the said dial, however, is sufficient to automatically release the makc-and-break device, which comprises the herein disclosed impulse wheel 21, and after the said make-and-break device has oncestarted to return to normal position, it cannot be stopped or restrained in its motion, but will continue in its operation until it has reached its normal position. When the dial is rotated to the point where its rotation is limited by the stop which engages the finger of the operator, then the slightest movement of the operators finger in a. direction to rotate the dial in a back ward direction .is snllicient to release the said make-and-brea-k device-that is to say, thcimpulse wheel 21-and then the return of the said impulse wheel to its normal position will continue uninterruptedly, as when once started in its return to normal position it cannot be stopped by the subscriber. In this way, as explained, the slow-acting relays of the two-wire telephone exchange system to which my invention relates are not subject to premature denergizing, and premature releases are not liable to happen, as an opening of the line circuit for the period of time required to denergize said relays and thereby effect the release is not liable to happen until the subscriber hangs up his telephone receiver.

It will be seen that by my invention the impulse-transmitting mechanism is absolutely prevented from being retailed in an off normal position after it has once started to return to normal position. Furthermore, andbecause. there is always a tendency toward a rebound or slight backward movemeut when the finger strikes the stop, my invention tends to preclude undue retention of the calling mechanism in any position to which it may be advanced by forward rotation of the dial. The tendency, therefore, is always to release the impulse-transmitting nzechanism as soon as the finger strikes the s op.

What 'I claim as my invention is 1; In a telephone system, a substation calling mechanism comprising a make-andbreak device, a dial for determining the degree of operation of said device, spring means for propelling said device, and means operative by slight backward movement of said dial for releasing said device to permit the same to return to normal while the dial remains at rest in its advanced position,

the makethere being means for opelritipfmmtim of and-break device by the the dial.

2. In a telephone system, a substation calling mechanism comprising a make-andbreak device, a dial for determining the degree of operation of said device, spring means for operating said device, and automatic means for releasing said device to permit the same to return to normal position while the dial remains at rest in its advanced position, there bein means for operating the make-and-break device by the forward rotation of the dial.

3. In a telephone system, a substation calling mechanism comprising a makeandbreak device, a dial for determining the degree of operation of said device, spring means for operating said device, means for locking said dial against forcible backward rotation, and means for releasing the device from said dial to permit the former to return to normal while the latter remains at rest in its advanced position, there being means for operating the make-and-break device by the forward rotation of the dial.

4. In a telephone system, a substation calling mechanism comprising a make-andbreak device, a dial for determining the degree of operation of said device, spring means" for operating said device, suitable connections by which the forward rotation of the dial correspondingly advances the said device, means for releasing said device to permit the sameto return to normal, and means for holding the said dial against backward rotation while the said device is thus returning to normal.

5. In a telephone system, a calling mechanism comprising a make-and-break' device, a dial for determining the degree of operation of said device, spring means for operating said device, and means tending to preclude undue retention of said device in any position to which it has been advanced by said dial, operative to release said device upon slight backward movement of the dial, for the purpose specified, there being means for operating the make-and-break device by the forward rotation of the dial.

6. In a telephone system, a closed line circuit, calling mechanism comprising a break and make device for opening and closin said line circuit at a normal rate of spec and means for preventing retention of said device in a condition to hold said circuit open for a period of time longer than the normal period 7. In a subscribers calling mechanism, a closed circuit, a rotary dial. means for operating the same,a spring-propellcd break and make device operated thereby for opening and closing said circuit at a normal rate of speed, and means for preventing interference with the operation of said break and make device to cause it to operate at a different rate of eed.

8. In a teephone system having a subscribers calling mechanism, the combination of a rotary dial, means for o crating the same, a spring-propelled brea and make device controlled thereby, means for locking the dial for preventing interference with the operation of said break and make device to cause it to operate at a difi'erent rate of speed, and a subscribers metallic line circuit controlled by said device.

9. In a subscribers calling mechanism, a make-and-break device, a dial for determin ing the degree of o eration of said device, means whereby sai dial can never rotate backward to normal position, mechanical connections between said dial and device whereby the forward rotation of the former correspondingly advances the latter, and means for releasing the said device to permit the same to return to normal.

10. In a subscribers calling mechanism, means for transmitting impulses, a rotatable dial for controlling said impulse transmitting means having an endless series of holes adapted to rotate in but one direction, a stationary series of numerals for said holes, and a-stop for variably limiting the rotation of said dial according to the hole selected.

11. In a subscribers calling mechanism, a dial rotatable only in one direction and provided with an endless series of holes, a make-and-break device automatically releasable from said dial, and a series of stationary numerals for said holes, there being means for operating the make-and-break device by the forward rotation of the dial.

12. In a subscribers calling mechanism, means for transmitting impulses, a stationary series of numerals for determining the degree of operation of said mechanism in calling, a member for controlling said impulse transmitting means rotatable only in one direction relatively to said numerals, and a stop for variably limiting the rotation of said member.

13. In a telephone system, a substation calling mechanism comprising a make andbreak device, a common battery transmitter connected in series with said make-and-break device and receiving current for talking purposes through the same, a dial for determining the degree of oplrirl'fition of said device, a stop for variably ting the rotation of said dial, spring means for propelling said device, and means operative y slight backward movement of said dial for releasing said device to permit the same to return to normal while the dial remains at rest in its advanced position, there being means for operating the make-and-break device by the forward rotation of the dial.

14. In a telephone system, a substation calling mechanism comprising a make-andbreak device, a common battery transmitter connected in series with said make-and-break device and receiving current for talking pur poses through the same, a dial for determining the degree of operation of said device, a stop for variably limiting the rotation of said dial, spring means for operating said device. and automatic means for releasing said device to permit the same to return to normal position while the dial remains at rest in its advanced position, there being means for operating the make-and-break device by the forward rotation of the dial.

15. In a telephone system, a substation calling mechanism comprising a make-andbreak device, a common battery transmitter connected in series with said make-and-break device and receiving current for talking purposes through the same, a dial for determining the degree of operation of said device, a stop for variably limiting the rotatlon of said dial, spring means for operating said device, means for locking said dial against forcible backward rotation, and means for releasing the device from said dial to permit the former to return to normal while the latter remains at rest in its advanced position, there being means for operating the make-and-break device by the forward rotation of the dial.

16. In a telephone system, a substation calling mechanism comprising a make-andbreak device, a common battery transmitter connected in series with saidmakeand-break device and receiving current for talking purposes through the same, a dial for determine ing the degree of operation of said device, a stop for variably limiting the rotation of said dial, spring means for operating said device, suitable connections by which the forward rotation of the dial correspondingly advances the said device, means for releasing said device to permit the same to return to normal, and means for holding the said dial against backward rotation while the said device is thus returning to normal, there being means for operating the make'and-break device by the forward rotation of the dial.

17. In a telephone system, a calling mechanism comprising a make-and-break device, a transmitter connected in series with said makc-and-break device and receiving current for talking purposes through the same, a dial for determining the degree of operation of said device, a stop for variably limiting the rotation of said dial, spring means for operating said device, and means tending to preclude undue retention of said device in any position to which it has been advanced by said dial, operative to release said device upon slight backward movement of the dial, for the purpose specified, there being means for operating the makeand-break device by the forward rotation of the dial.

18. In a telephone system, and in combination with means for connecting subscribers and whereby the release is effected by the opening of the subscribers metallic line circuit, when the receiver is hung up, a calling mechanism comprising a make-andbreak device, a common battery transmitter connected in series with said make-andbreak device and receiving current for talking purposes through the same, and means for preventing retention of said device in a condition to hold the circuit open for an undue period of time to prevent a premature release.

19. In a subscribers calling mechanism, the combination of a rotary dial, a stop for variably limiting the rotation of said dial, a sprin -propelled make-and-break device associated therewith, means for preventing interference with the operation of said makeand-break device, and a common battery transmitter connected in series with said make-and-break device and receiving current for talking purposes through the same.

20. In a telephone system having a subscribers calling mechanism, the combination of a rotary dial, a stop for variably limiting the rotation of said dial, a springpropelled make-and-break device, means for preventing interference with the operation of said make-and-break device, a common battery transmitter connected in series with said make-and-break device and receiving current for i. talking purposes through the same, and a subscribers metallic line circuit controlled by said device.

21. In a subscribers calling mechanism, a make-and-brea-k device, a common battery transmitter connected in series with said make-and-break device and receiving current for talking purposes through the same, a dial for determining the degree of operation of said device, a stop for variably limiting the rotation of said dial, means whereby said dial can never rotate backward to normal position, mechanical connections between said dial and device whereby the forward rotation of the former correspondingly advances the latter, and means for releasing the said device to permit the same to return to normal.

22. Ina subscribers calling mechanism, means for transmitting impulses, a dial rotatable only in one direction, for controlling said impulse transmitting means having an endless series of finger holes, a finger stop for variably limiting the rotation of said dial, and a stationary series of numerals for said-holes.

23. Ina subscribers calling mechanism, a dial rotatable only in one direction and provided with an endless series of holes, a stop lad for variably limiting the rotation of said dial, a make-and-break device automatically releasable from said dial, a common battery transmitter connected in series with said make-and-break device and receiving current for talking purposes through the same, and a series of stationary numerals for said holes, there bein means for operatin the make-and-break evice by the forwar rotation of the dial.

24. A telephone exchange system impulse transmitter comprising a. dial, an impulse wheel, means for returning the wheel to normal osition, means for holding the dial locked in its advanced position, and means for releasing the dial when the wheel reaches its normal position.

25. In a telephone system, a subscribers calling dial, an impulse wheel, means for returning the wheel to normal position,

means for holding the dial locked in its advanced position, means for releasing the dial when the wheel reaches its normal position, and means for normally locking the dial against rotation.

26. In a two-wire telephone exchange system, a calling dial therefor, an impulse wheel, means for returning the wheel to normal position, means for holding the dial locked in its advanced position, means for releasing the dial when the wheel reaches its normal position, and normally closed line springs adapted to be opened and closed to transmit the impulses.

Signed by me at Chicago, Cook county, Illinois, this 15th day of February, 1908.

BETHUEL M. DAVIS.

Witnesses:

Enwann D. FALER, Jmmm NonBY.

Copies of this patent may be obtained for five cents each, by addressing the Commissioner of Yatents,

Washington, D. 0.

Corrections. in Letters PatentNo. 1,146,786.

It is hereby certified that in Letters Patent No. 1,146,786, granted July 20, 1915, upon the application of Bethuel M. Davis, of Chicago, Illinois, for on improvement .in Tele hone S stems, errors a. car in the rinted s ecification re uirin cor- P 3'' PP P P q 8 rection as follows: Page 6, strike out the sentence commencing with the word When, line 48, and ending with the compound word "trunk-line, line 54; same page, line 84, for the word contcat reed contact; page 8, line 106, for the word retailed read retained; and that the said Letters'Patent-should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 7th day of September, A. D., 1915.

J. T. NEWTON,

Acting Commissioner of Patents.

[SEAL-l 

